1. Field of the Invention
The present invention relates to a sensor control device provided with a potential reference terminal and a potential output terminal, the sensor control device applying a voltage to a sensor element connected between the potential reference terminal and the potential output terminal.
2. Description of the Related Art
A sensor control device provided with a potential reference terminal and a potential output terminal has been used to apply a voltage to a sensor element connected between the potential reference terminal and the potential output terminal.
An example of such a sensor control device is an NOx sensor control device that applies a voltage to an NOx sensor as disclosed in WO03/083465 (FIG. 1 and FIG. 8).
The NOx sensor control device applies a voltage to the NOx sensor element (Ip2 cell) connected between the potential reference terminal (Vcent terminal) and the potential output terminal (Ip2 terminal) by setting the potential of the potential reference terminal (Vcent terminal) to be a reference point target potential, and by setting the potential of the potential output terminal (Ip2 terminal) to be an output point target potential.
Both the reference point target potential and the output point target potential are set in such a manner that the voltage applied to the NOx sensor element (Ip2 cell) remains at the target-applied voltage.
In the sensor control device in the related art, however, even in the case where the potential of the potential output terminal (Ip2 terminal) is set to be the output point target potential at a high degree of accuracy, there is a possibility that the actual voltage applied to the sensor element assumes a voltage value different from the target applied voltage. This can occur when the potential of the potential reference terminal (Vcent terminal) fluctuates due to influence of noise or the like.
More specifically, because the sensor control device in the related art is configured so that the potential of the potential terminal (Ip2 terminal) and the potential of the potential reference terminal (Vcent terminal) are independently controlled, a problem arises in that even when the potential of the potential output terminal (Ip2 terminal) is set at a high degree of accuracy, the voltage applied to the sensor element varies when the potential of the potential reference terminal (Vcent terminal) fluctuates.